What CDM asks for
On any project with more than one contractor, CDM 2015 requires a health and safety file. It records the information someone will need to carry out future construction work on the building safely, and it stays with the client afterwards.
The principal designer prepares it. If their appointment ends before the project does, responsibility passes to the principal contractor. The client has to keep it available.
None of that is controversial. What causes trouble is that the file is only useful if it reflects what was actually built.